In the process of manufacturing ICs with LSI, VLSI and ULSI, patterned material layers are produced by photolithographic techniques. Nowadays, such patterned material layers comprise structures of dimensions even below 20 nm with high aspect ratios.
Photolithography is a method in which a pattern on a photo mask is projected onto a substrate such as a semiconductor wafer. Semiconductor photolithography typically includes the step of applying a layer of a photoresist on a top surface of the semiconductor substrate and exposing the photoresist to actinic radiation, in particular UV radiation of a wavelength of, for example, 193 nm or 13.5 nm, by using a transmission or reflective photo mask.
As technologies advance and dimension requirements become stricter and stricter, photoresist patterns are required to include relatively thin and tall structures or features of photoresists, i.e., features having a high aspect ratio, on the substrate. With the shrinking of the dimensions of the structures on the substrate itself also the dimensions of the photo mask need to shrink.
The current cleaning processes (O3, SC1 & ultra pure water for 28 nm) do also not provide mask surfaces that are free from contamination (Haze defect generation).
WO 2012/101545 A discloses the use of surfactants having at least three short-chain perfluorinated groups Rf for manufacturing integrated circuits (ICs), in particular, ICs having large-scale integration (LSI), very-large-scale integration (VLSI) and ultra-large-scale integration (ULSI), the said ICs having high aspect ratio patterns with line-space dimensions below 50 nm.
As semiconductor manufacturing advances to sub-20 nm node (i.e., minimum feature pitch) technology, specifications with respect to ‘dust’ on photo masks are becoming even more stringent. As a rule of thumb the photo mask patterns of transparent photo masks, like that for 193 nm immersion lithography, need to be about 4 to 5 times bigger than the minimum feature size to be printed on the micro device wafer. This means that for a 20 nm feature to be printed on the device wafer, the minimum feature size of the photomask has to be 80 to 100 nm while keeping a high aspect ratio above 1.
Photo mask cleanliness is essential to high-quality lithography. Detecting a single newly introduced particle following pellicle (protective cover) mounting may result in a loss of one to two days for demounting, repairing, and cleaning of the photo mask as well as yield loss (as defects will be transferred during the exposure process to the wafer). A major challenge in developing sub-20 nm node mask cleaning processes is therefore the removal of extremely fine particles (<50 nm) from the photo mask surface.
New photo mask cleaning processes are required to remove and eliminate particles on photo masks and to remove contaminants that can cause defect formations. Typical cleaning processes work by under-etching the particle which stays on the surface, i.e. by under-etching the particle is removed from the surface. The under-etching needs to be as low as possible in order to reduce the attack of the substrate surface to avoid Critical Dimension (CD) loss and increase of surface roughness.
It is therefore an object of the present invention to provide a further use for fluorosurfactants containing at least three short-chain perfluorinated groups Rf and/or pentafluorosulfanyl groups.
It is a further object of the present invention to provide a process for preparing photo masks without causing damage of the patterned photo masks.
It is yet another object of the present invention to provide an improved photolithographic process which allows for the photolithography of photoresist layers with reduced defects.